In recent years, ceramics have been aggressively studied for use as structural parts because of their superiority over metals with respect to heat resistance, strength, hardness, and corrosion resistance. Inter alia, silicon carbide ceramics, which are excellent in strength, hardness, and corrosion resistance, have already been put to practical use in some fields such as mechanical seals or sliding parts (such as bearings). However, the range of applicable uses in sliding parts has been limited due to poor sliding characteristics in dry atmosphere and low thermal shock resistance.
Incorporation of a lubricating filler, e.g., carbon and graphite, into silicon carbide is one approach to improving the sliding characteristics of ceramics. For example, incorporation of granular graphite into ceramic materials is proposed in JP-A-63-260861 (the term "JP-A", as used herein, means an "unexamined published Japanese patent application") under the title "Self-Lubricating SiC-Graphite Ceramics", and JP-A-63-265850, under the title "Self-Lubricating Ceramic Composite Materials and Process For Producing The Same"; and incorporation of self-sintering carbonaceous fine spherical particles is proposed in JP-A-3-33064 under the title "Powder Composition For Producing Carbon-Silicon Carbide Composite Material, A Process For Producing Carbon-Silicon Carbide Composite Material, and Carbon-Silicon Carbide Composite Material".
According to these techniques, however, incorporation of carbon or graphite particles, though successful in reducing the sliding coefficient of friction, reduces the density and strength, resulting in impairment of characteristics essential to ceramics. Thus, the resulting composite materials have poor durability.
JP-A-1-320254, entitled "Carbon-Filled Ceramic Composite Material and Process For Producing The Same", discloses a method for optimizing the degree of graphitization of carbon present in a composite material by means of X-ray diffractometry. Although the resulting composite material has excellent sliding characteristics and strength, the optimum condition of the carbon present in the composite material and the optimum source of carbon are not specified, and the composite material has poor thermal shock resistance. Moreover, the process for production involves a complicated step of calcination under pressure and is, therefore, unsuitable for industrial production.